1. Field of the Invention
The invention relates to an uninterruptible power supply system and device, and more particularly to a direct-current uninterruptible power supply system and device of a direct-current power source.
2. Description of the Related Art
Referring to FIG. 1, a conventional uninterruptible power supply device 1 includes a voltage distribution unit 11 that converts electrical power from a three-phase alternating-current (AC) power source 300 to single-phase electrical power, and a power supply unit 13 that converts the single-phase electrical power provided by the voltage distribution unit 11 to direct-current (DC) electrical power. The DC electrical power outputted by the power supply unit 13 is provided to a server 200, and also to a charging circuit 31 that converts the DC electrical power to a rating voltage of a battery 33 for charging the battery 33. The battery 33 is coupled to a transformer module 35. A switch 37 is coupled between the transformer module 35 and the server 200 and is controlled by the power supply unit 13. When the AC power source 300 stops output of electrical power, the power supply unit 13 controls the switch 37 to make electrical connection between the transformer module 35 and the server 200, so that the battery 33 outputs electrical power that is subsequently converted by the transformer module 35 to DC electrical power required by the server 200. The converted DC electrical power is then provided to the server 200 through the switch 37, thus achieving uninterrupted power supply.
However, the conventional uninterruptible power supply device 1 is only suitable for a single load, and cannot be connected to another uninterruptible power supply device, so that the load of the another uninterruptible power supply device cannot obtain additional electrical power when required. Furthermore, the transformer module 35 of the conventional uninterruptible power supply device 1 is usually implemented using a switching DC-DC converter, which is relatively complicated and has a relatively large size, making it difficult to reduce the size of the uninterruptible power supply device 1, and thus disfavoring application to electronic products that tend to have a light weight and a small size.